Refractory



l v u U s Dec. 15, 1953 H. o. KAUFFMANN ETAL 2,662,825

' REFRACTORY Filed June 5, 1948 [WE/7T0? Han: 0. Kaufi'mann and Jame: f.W/za/en, Jr.

Patented Dec. 15, 1953 REFRACTORY" Wanda, NY.

Claims.

The present invention relates to the manufacture of refractory productsand more particularly to ceramic products containing a multitude ofcavities or cells which render such products suitable for employmenteither as a sound-absorbing media or as improved heat-insulating media.

Refractory pgrous products have been made heretofore by incorporatingcombustible organic materials as, for instance, coke, sawdust, cork,resinous materials, and the like, in aslurry of materials which arecapable of providing the desired refractory composition. After theslurry has been molded into desired hape for the resulting moldedobjects, the green bonded products are fired at a relatively lowtemperature to burn out and destructively distill off substantially allof the combustible material initially mixed with the slurry. In thisfashion have been prepared refractory bricks having certain desiredproperties, as for instance, suitable resistance to crushing forces andhaving, due to the internal cavities, a weight constituting only 40 to25% of the weight of a non-porous refractory. The porosity of theresultant brickresults in desired physical properties, for instance,excellent heatinsulating qualities.

However, during the process of burning out the combustible materialtoform a cellular structure, the molded articles ordinarily tend to crackby reason of the fact that channels are produced in the article by theproducts of destructive distillation in order to escape from theinterior to the exterior of the article. Asa consequence, the productionof faulty bricks or "seconds in the manufacture of such brick isrelatively highand,

Q is not of a desired high grade.

is an object of the present invention to provide improved channel-freeporous stony refractory articles in which the porous nature of thearticle is characterized by small uniformly distributed individual poresor cells. Our invention also comprises a. method for fabricating sucharticles which does not result in cracking. It is a further object ofour invention to provide an improved procedure wherein a predeterminedamount of gaseous material is developed within a preliminary set orgreen product, that is, prior to firing the green-bonded article toresult in ceramic maturation. As a consequence, we have provided aprocedure for reducing to a minimum the amount of cracking duringfiring, thus efiecting a reduction in the production-of seconds.

In accordance-with the b road concept of om in general, homogeneity ofthe finished products Hans 0. Kaufimann, Eggertsville, and Jamal.Whalen, Jr., Kenmore, N. Y., ass-ignore to Buf falo Electro-ChemicalCompany, Inc., Tona- Application J une 5, 1948, Serial No. 31,286

invention, a product is prepared from arslurry including arefractorygnaterial and an gugganic sejti ng matprial which is capableoi acting as a green bond to produce-an initial set or solidification ofthe slurry, after the same has been molded into the desired shape by anyconventional molding procedure. In addition to the bonding agent,another component of a slurry embodying the present invention is aproduct capable of gene:- ating a gaseous material as small bubblmst'riuted throughout the slurry and, hence. in the green. bond. The slurrymay contain, as .a gas yielding component, an inorganic peroxide :0! theclass of hydrogen pe r9xide, alkali metalpeggxides, and alkalineearthgietaL-pggoxige or a suitable mrsalt capable of generatingjhydrogenperoxide in aqueous solution. As later more fully stated, a decomposingagent for theperqigide also is present.

The accompanying drawing shows, in Fig. l, a photo-micrographiccross-section of a cellular product which was prepared by the priordestructive distillation method heretofore described and, in Fig. 2, aphoto-micrographiccross-section of a product embodying the presentinvention.

The refractorycoglponen may be selected'in accordance with the properies desired for the final product andmayconsistof the generally usedrefractories such as silica, alumina, or the refractorysilicates, as forinstance, zirconium silicate or refractory clays. To the chosen-re- Lfractoryis added water and a setting agent as, for example, a minoramount of wiping; sum, These components are proportioned in quantity toproduce a plastic mix capable of being preformed into the desired shapeosmlding, ramming or other conventional shaping procedure. In general,the gas-yielding material employed will be hydrogen peroxide. It

may be added at a suitable time to the mixture before the setting agenthas solidified. For example, after the slurry has been made and while itstill is semi-liquid or plastic, a suitable amount of aqueous solutionof hydrogen peroxide is mixed uniformly therewith and then the peroxideis decomposed catalytically into oxygen and water. By reason of theuniformity of distribution of the peroxide, the evolution of oxygen gasproceeds in uniform fashion throughout the body of the aqueous plasticor semi-solid slurry. Gas evolution should be complete prior to the timethat the calcined gypsum takes its initial set. This operation may beperformedat approximately room temperature.

After the cast refractory has taken its initial set by the change of thecalcined gypsum from the hemihydrate condition to the dihydratecondition, the molded articles are removed to a kiln where they aresubjected to a temperature high enough to drive 011 water of hydration.A suitable temperature for such drying and baking is 230 F., butsomewhat lower or higher temperatures may be used. The baked articlesare subiected subsequently to a firing cycle, the temperature of whichis sufilciently high and the duration of which is of sufficient lengthto induce ceramic sintering or vitrification of the mass as desired. Thetemperature of firing or maturation will depend upon the character ofthe component which is employed as refractory, and upon the propertiesdesired in the finished article as is well understood in the manufactureof ceramic products. In some cases, a firing temperature of 1600 F. issuitable and, in other cases, a firin temperature of 2300 F. isemployed.

The decomposition of the hydrogen peroxide should be completed prior tothe time when the article is subjected to the ceramic firing and,therefore, the catalytic decomposition of the peroxide must beconsummated within the short period of time required for the calcinedgypsum to set, namely, a matter of a few minutes to a time as short asfractions of a minute. In order to properly accomplish suchdecomposition it has been found thatlthe inclusion at proper pH u amountold 1 oan csa s are Me an. The salts chosen for this purpose may be thesolubleiaitshiwe, of cobalt, .nhimnnofni lidlan antia luame L l b.221.wfl i i j lfi flli fi u filfl taneous decomposition of hydrogenperoxide. Manganous salts, as for exampleg anganous sulfate or chloride,will be found especially efiective and desirable. In order to obtainsubstantially instantaneous evolution of gaseous oxygen from thepore-forming peroxide, the pH of the mixture should be above H 8 andpreferably in the range H 8 to 10.

The relative proportion of clay or other chosen refractory material andgypsum, or other chosen hydrosetting material, is governed by therequirements. If high pre-firing strength is desired, a relatively highratio of hydrosetting material is chosen. On the other hand, if a highdegree of temperature-resistance or refractoriness is desired, a lowerratio of hydrosetting material and correspondingly higher ratio ofceramic material may be chosen. Two parts of ceramic material to onepart of hydrosetting material by weight is a suitable ratio.

' The amount of gas-evolving agent is determined by the porosity desiredin the finished product. By weight (based on the weight of the clay),suitable limits are 0.1 to 0.4% of hydrogen peroxide. The decomposingagent, based on manganous sulfate with 4H2O, may be chosen within limitsof 0.05 to 0.25% by weight. Qrdinarily the amounts of gas-evolving agentand decomposing agent are chosen to produce cavities of a diameter of0.01" to 0.04" in the final product.

The following example is to be considered illustrative of the inventionand is not to be deemed limitative thereof, as it will be understoodthat the amounts of ingredients and the ingredients themselves may bevaried over relatively wide ranges, as pointed out, without departingfrom the spirit and scope of the invention.

4 In Table I, stating the ingredients in units of weight and volume,small scale units were chosen for illustrative purposes:

Ingredients by weight and volume 200 g. clay g. gypsum 275 cc. water 5cc. of an alkyl aryl sulfonate, such as Naceanol .N. R. (10% solution) 2cc. sodium hydroxide (10% solution) 2 cc. 100 vol. hydrogen peroxide 3cc. Manganous sulfate (10 solution of crystals containing 4H 2O Sameingredients wholly by weight The weight 'of water in Table 2 includeswater of solution.

The clay and gypsum are mixed intimately in the dry state by passagethrough a ball mill, although it will be understood that any otherconventional form of mixing may be employed. The mixed products in thedry state are poured into a solution of sodium hydroxide in the amountof water specified, to which had been added a suitable wetting agent orintrofier. A composition of alkyl aryl sulfonate may be used as aWetting agent, such as Nacconal N. R. Other known wetting agents, suchas sulfates of long chain alcohols, may be used. In general, organicwetting agents are preferred to soaps. Mixing should be performed underconstant stirring until a creamy consistency is obtained. Thereafter,the specified amount of hydrogen peroxide is added and thoroughlydistributed throughout the mix. Lastly, the decomposition catalystshould be added. The volume of the mix expands as a foamy, plastic masswhich may be formed, without delay, for example, by being cast intomolds where the inorganic gypsum bond is permitted to set, thusentrapping the evolved oxygen and maintaining the green moldedcomposition in porous form. 1

The molded article may be removed from the molds, transferred to a kilnand slowly heated to a suitable drying temperature, e. g., 212 to 230 F.and, in some cases, in the neighborhood of 300 F. When the bakedarticles are dry, the firing cycle is carried out. The temperature, forexample, may be chosen as heretofore stated in the range of about 1600to 2300" F. or higher, until ceramic sintering or fusion is complete.

Referring to the drawing which shows, in Fig. 1, a, section of a porousceramic product such as produced prior to our invention and which shows,in Fig. 2, a section of a product embodying our invention, it isapparent that a novel porous structure has been produced. The structureof the porous articles as heretofore produced, Fig. 1, contain numerousrelatively large cavities and the structure of the compositionsurrounding the large cavities contains both disproportionately minutecavities and thick walls devoid of cavities.

The new product, Fig. 2, is finer grained and is filled with cavities oiuniform size and distribution. The practical consequence of the improvedstructure are improved strength, less waterabsorptiveness and excellentinsulating and refractory properties.

What is claimed is:

1. A molding composition for the manufacture of ceramic ware comprisingthe combination by weight of about 200 parts of refractory clay, 100parts of calcined gypsum, 300 parts of an aqueous solution containingabout 0.10 to 0.40% of an inorganic peroxide and about 0.05 to 0.25% ofa catalyst of decomposition for the peroxide, said solution alsocontaining an introfier and sufiicient alkali to produce a pH in therange 01' about 8 to 10.

2. A molding slurry for the production of cellular brick comprising thecombination by weight of about 200 parts of refractory clay, about 100parts of'calcined gypsum and about 300 parts of an aqueous solutionhaving a pH 8 to 10, and having dissolved therein about 0.3% of hydrogenperoxide. 0.15% of MnSO4-4H2O, and about 0.25% or an introfier.

3. A method of fabricating ceramic cellular products which consists informing a slurry consisting of an aqueous suspension of a refractoryclay in major proportion, a calcined gypsum, an inorganic peroxide andan introfier, molding such slurry into desired form while charged withgas bubbles derived from said peroxide, drying the resulting solidifiedporous product and firing at elevated temperature to cause conversion ofsaid refractory clay to a ceramic condition.

4. A method of making porous ceramic products which consists in forminga slurry containing as major components a refractory clay,

calcined gypsum in amount less than the clay but sumcient to form agreen bond therefor and water as a liquid suspending medium, said mediumconsisting of an aqueous solution containing about 0.20% of hydrogenperoxide, about 0.05 to 0.25% of a catalyst of decomposition for saidperoxide, an introfier and suflicient alkali to result in a pH range of8 to 10, causing said slurry to set in desired form while charged withgas bubbles derived by the decomposition of the hydrogen peroxidecomponent, drying the resulting objects and thereupon firing saidobjects at a maturing temperature whereby a ceramic is produced.

5. A molding composition for the manufacture of porous ware comprisingan aqueous suspension of a refractory clay in major amount, and calcinedgypsum in minor amount, said suspension being alkaline and containing aninorganic peroxide, a catalyst of decomposition for the peroxide and anintrofier.

HANS O. KAUFFNLANN. JAMES F. WHALEN, JR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date Re. 17,523 Ericson Dec. 17, 1929 2,399,225 Heany Apr. 30, 1946FOREIGN PATENTS Number Country Date 315,205 Great Britain 1929 363,192Great Britain 1931 539,022 Great Britain 1941 129,784 Austria 1932

5. A MOLDING COMPOSITION FOR THE MANUFACTURE OF POROUS WARE COMPRISINGAN AQUEOUS SUSPENSION OF A REFRACTORY CLAY IN MAJOR AMOUNT, AND CALCINEDGYPSUM IN MINOR AMOUNT, SAID SUSPENSION BEING ALKALINE AND CONTAINING ANINORGANIC OXIDE AND AN INTROFIER.